1. Field of the Invention
This invention relates to novel piperazine derivatives, and more specifically to piperazine derivatives represented by the general formula (I) and their acid addition salts: ##STR2## wherein
R.sub.1 : an indolyl group which may optionally be substituted by one or more lower alkyl and/or lower alkoxy groups, naphthyl group which may optionally be saturated partially with 2 or 4 hydrogen atoms, or phenyl or cyclohexyl group which may optionally be substituted by one or more lower alkyl groups;
A: a single bond or alkylene group;
P: a single bond or vinylene group;
Q: an --O--alkylene group or --NH--alkylene group when P is a single bond, or a single bond when P is a vinylene group; and
R.sub.2 : a lower alkyl, morpholino-lower alkyl, morpholinocarbonyl lower alkyl, piperidinocarbonyl lower alkyl, piperazinocarbonyl lower alkyl or lower alkylaminocarbonyl lower alkyl group.
2. Prior Art
The present inventors have synthesized a variety of compounds and have investigated their enzyme inhibitory activities so as to develop proteolytic enzyme inhibitors.
As a result, it has been found that novel piperazine derivatives of the formula (I) above and their acid addition salts have unexpectedly excellent inhibitory effects against chymotrypsin, trypsin and thrombin. This finding has led to the present invention.